Tagging-Gas Failed Fuel Detection and Location System for Sodium-Cooled Reactors

Abstract

Failed fuel detection for the Japan Sodium-cooled Fast Reactor (JSFR) has been studied. The present JSFR design adopts a selector-valve (SV) failed fuel detection and location (FFDL) system. In this study, a tagging-gas (Tag) FFDL (Tag-FFDL) system has been investigated as an alternative. Although the identification performance of the Tag-FFDL system has been demonstrated in small and medium-sized reactors, the Tag-FFDL system has not been demonstrated yet in a large reactor like JSFR, which has 1500-MW(electric) power and 562 core fuel subassemblies. Major issues of the JSFR Tag-FFDL system are affected by high-burnup fuel and large cover gas volume. High-burnup fuel leads to a large change of the isotope ratio, which is important for the detection performance of the Tag-FFDL system. Since the cover gas volume in JSFR is larger than that in previous reactors, the tagging-gas concentration in the cover gas is lower than that in previous reactors. Thus, a requirement of the background value is more strict in JSFR. This study investigates whether two issues of the Tag-FFDL system for JSFR would be solvable. Tag gas isotope change in a high-burnup condition has been evaluated regarding transmutation and fission gas release. Taking into account tag gas isotope change due to the high-burnup conditions and large cover gas space, JSFR tagging gas has been designed. The investigation results showed that the JSFR FFDL system can provide an identification capability for 672 subassemblies, which is larger than the number of subassemblies in JSFR combining tagging-gas and burnup estimation. In addition, an allowable background concentration of natural Kr and Xe in the cover gas has been evaluated.